White LED package structure having a silicon substrate and method of making the same

ABSTRACT

A white light emitting diode package structure having a silicon substrate is disclosed. The white light emitting diode package structure comprises a silicon substrate having a plurality of cup-structures thereon, one of a plurality of blue light emitting diodes is respectively disposed in each cup-structure, and a phosphor structure covering the silicon substrate and the cup-structures. The blue light emitting diodes have various wavelengths and the phosphor structure has a plurality of kinds of phosphor powders and a sealing material. Each kind of phosphor powder is able to convert blue light within a certain wavelength into yellow light.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a white light emitting diode (LED)package structure and a method of making the same, and moreparticularly, to a white LED package structure having a siliconsubstrate with good thermal conductivity and good light condensation toraise the color rendering and the colorfulness of tone and a method ofmaking the same.

2. Description of the Prior Art

In recent years, a white LED is a new product that is most expected andfocused on worldwide. The white LED has advantages of small volume, noradiation, low power consumption, long lifetime, fast response rate andfunctions of environment protection etc., and also can solve many pastproblems that incandescent lamps could not overcome. Therefore,scientists in Europe and America have served the white LED as a lightsource in 21 century.

Please refer to FIG. 1. FIG. 1 is a cross-sectional schematic diagram ofa white LED package structure according to the prior art. The white LEDpackage structure 10 comprises a blue LED 11, a substrate 12, twoelectrodes 13, 14, a conductive layer 15 and a phosphor structure 16.The blue LED 11 is a main light-emitting element of the white LEDpackage structure 10. The conductive layer 15 can be disposed on thesubstrate 12 by the process of metal deposition, exposure andlithography etc., and the blue LED 11 can be electrically connected tothe electrodes 13, 14 through the conductive layer 15. The phosphorstructure 16 is used for preventing the blue LED 111 from being directlyexposed to the exterior, and the phosphor powders doped in the phosphorstructure 16 including epoxy resin has a function of absorbing the bluelight and converting blue light to yellow light. Therefore, a portion ofblue light emitting from the blue LED 11 will be absorbed and convertedto yellow light by the phosphor structure 16, and the yellow light willbe mixed with the other portion of the blue light so that white light isproduced.

The defect in current technology is that only one blue LED is disposedin the white LED package structure 10. If a brighter illumination or alarger size of light source is required, to combine several white LEDpackage structures 10 is necessary. However, one white LED packagestructure 10 has a specific size, so the size of the light source ismuch larger. In addition, the full width at half maximum (FWHM) of thewavelength of one blue LED is about 25 nm. In manufacturing process, agreat deal of the blue LEDs cannot be made to all have the samewavelength. Therefore, the produced blue LEDs currently can be dividedinto three specifications by the wavelengths of the blue LEDs, and thespecifications are 450±5 nm, 460±5 nm and 470±5 nm. In accordance withthe three specifications, the three corresponding phosphor powders arerespectively created to produce the white LED. However, because thecondition of manufacturing the blue LEDs is not easy to control, thewavelength of the blue LED will easily have a deviation effect. Evenusing the blue LED with the same specification, the produced white LEDsstill will have various tones of the white light. The color rendering ofthe white LED is lower than that of fluorescent lamps and incandescentlamps, and the colorfulness of tone of the white LED is, too. Therefore,to produce a white LED having high color rendering and colorful tone tomatch the natural light is an object that needs the industry to improve.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a whiteLED package structure that has better thermal conductivity andcondensation of light and raises the color rendering and thecolorfulness of tone and a method of making the same.

According to an embodiment of the present invention, a white LED packagestructure having a silicon substrate is provided. The white LED packagestructure having a silicon substrate comprises a silicon substratehaving a plurality of cup-structures thereon, a reflective layercovering a top surface of the silicon substrate, a transparentinsulating layer covering the reflective layer, a plurality of metalbumps respectively disposed on the transparent insulating layer in eachcup-structure, a plurality of electrodes disposed on the siliconsubstrate between the cup-structures, a plurality of blue LEDs having aplurality of various wavelengths respectively disposed on each metalbump in each cup-structure, and a phosphor structure covering thecup-structures of the silicon substrate. The blue LEDs are electricallyconnected to the electrodes. The phosphor structure comprises aplurality of kinds of phosphor powders and a sealing material, and eachkind of the phosphor powder is capable of converting blue light withincertain wavelength into yellow light.

According to an embodiment of the present invention, a method of makinga white LED package structure having a silicon substrate is provided.The method comprises providing a silicon substrate and performing anetching process to form a plurality of cup-structures on a top surfaceof the silicon substrate. Next, a reflective layer on the top surface ofthe silicon substrate is formed, and a transparent insulating layer onthe reflective layer is formed. Then, a plurality of metal bumps on thetransparent insulating layer in each cup-structure is formed, and aplurality of electrodes on the transparent layer between the adjacentcup-structures is formed. Subsequently, a plurality of blue LEDs arerespectively bonded on the metal bumps in each cup-structure, andelectrically connected respectively to the electrodes, wherein the blueLEDs have various wavelengths. Last, a plurality of kinds of phosphorpowders corresponding to the wavelengths of the blue LEDs are mixed witheach other and added to a sealing material, and a sealing process isperformed to form a phosphor structure on the cup-structures.

According to another embodiment of the present invention, a method ofmaking a white LED package structure having a silicon substrate isprovided. The method comprises providing a silicon substrate, andperforming an etching process to form a plurality of cup-structures on atop surface of the silicon substrate. Next, a reflective layer is formedon the top surface of the silicon substrate, and a transparentinsulating layer is formed on the reflective layer. Then, a conductivelayer is formed on the transparent insulating layer, and a plurality ofblue LEDs are respectively bonded on the conductive layer in eachcup-structure, wherein the blue LEDs have various wavelengths. Last, aplurality of kinds of phosphor powders corresponding to the wavelengthsof the blue LEDs are mixed with each other and added to a sealingmaterial, and a sealing process is performed to form a phosphorstructure on the cup-structures.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional schematic diagram of a white LED packagestructure according to the prior art.

FIG. 2 is a cross-sectional schematic diagram illustrating a white LEDpackage structure having a silicon substrate according to a preferredembodiment of the present invention.

FIG. 3 is a top view illustrating the white LED package structure shownin FIG. 2.

FIG. 4 is a cross-sectional schematic diagram illustrating a white LEDpackage structure having a silicon substrate according to anotherembodiment of the present invention.

FIGS. 5-10 are schematic diagrams illustrating a method of making awhite LED package structure according to a preferred embodiment of thepresent invention.

FIGS. 11-16 are schematic diagrams illustrating a method of making awhite LED package structure according to another preferred embodiment ofthe present invention.

DETAILED DESCRIPTION

Please refer to FIG. 2 and FIG. 3. FIG. 2 is a cross-sectional schematicdiagram illustrating a white LED package structure having a siliconsubstrate according to a preferred embodiment of the present invention.FIG. 3 is a top view illustrating the white LED package structure shownin FIG. 2. The white LED package structure 100 includes a siliconsubstrate 110, a reflective layer 120, a transparent insulating layer130, four metal bumps 140, a plurality of electrodes 150, four blue LEDs160 and a phosphor structure 170. The material of the silicon substrate110 can be polycrystalline silicon, amorphous silicon or monocrystallinesilicon, and the silicon substrate 110 can be a rectangular silicon chipor a circular silicon chip. In addition, the silicon substrate 110 mayinclude integrated circuits or passive components therein. A top surfaceof the silicon substrate 110 has four concave cup-structures whose topviews are rectangular, and each cup-structure has inclined sidewalls.The inclined sidewalls of each cup-structure are used to reflect thesidelight emitted from the side surfaces of each blue LED 160 and changethe direction of the sidelight to emit to the exterior so that the lightutility is increased.

The reflective layer 120 is disposed on the top surface of the siliconsubstrate 110. The material of the reflective layer 120 is metal or anoptical thin film that makes the sidewalls of the cup-structures havegood reflectivity to reflect the sidelight from the side surfaces of theblue LED 160. However, in order to insulate the reflective layer 120from devices disposed thereon, the transparent insulating layer 130 isdisposed on the reflective layer 120 so that the reflective layer 120 iselectrically disconnected from the metal bumps 140 and the electrodes150. Each metal bump 140 is respectively disposed on the transparentinsulating layer 130 in each cup-structure, and each metal bump 140 isused to connect each blue LED 160 and each cup-structure. Each blue LED160 is disposed on each metal bump 140, and the positive electrodes andnegative electrodes of the blue LEDs 160 are respectively electricallyconnected to the electrodes 150 through a plurality of wires 180.

In addition, the blue LEDs 160 respectively have various wavelengthsincluding three specifications of 450±5 nm, 460±5 nm and 470±5 nm inorder to provide a high color rendering for the white LED packagestructure 100. The electrodes 150 are disposed on the silicon substrate110 between the cup-structures, and the function of the electrodes is toelectrically connect the white LED package structure 100 to externalcircuits (not shown in figure). The phosphor structure 170 covers thecup-structures and fills up each cup-structure, and the shape of thephosphor structure 170 is a flattop pyramid-shaped. The top surface andsidewalls of a flattop pyramid respectively are flat and inclined. Inaddition, the phosphor structure 170 includes a plurality of kinds ofphosphor powders and a sealing material. Each kind of the phosphorpowder is created in accordance with the specifications of the blue LEDs160, so each specification of the blue LEDs 160 is corresponding to onekind of phosphor powder. Each kind of phosphor powder is able to convertblue light within a certain wavelength emitted from one blue LED 160into yellow light. The sealing material includes epoxy resins andsilicon fillers, and the sealing materials can be divided into an epoxymolding compound used in molding processes and a liquid encapsulant usedin encapsulating processes.

The cup-structures on the top surface of the silicon substrate 110 arearranged in a rectangular array, and the distance between the edges ofthe adjacent cup-structures is short, substantially smaller than 10 μm.Because the blue LEDs 160 are disposed in a short distance between theedges of the cup-structures, the effect of interference will not happenwhen the light emitted from the blue LEDs 160 are mixed with each other.In addition, due to the short distance arrangement of thecup-structures, the light pattern of the white LED package structure 100can be highly uniform. It is saying that the light pattern from fourdifferent blue LEDs 160 disposed in a short distance between theadjacent cup-structures can be the same as the light pattern emittedfrom one blue LED whose size is the same as the total size of the fourblue LEDs 160. Also, the light of the blue LEDs 160 having variouswavelengths can be mutually mixed, so the white LED package structure100 having high color rendering can be achieved. In addition, becausethe material of the silicon substrate 110 is silicon, the white LEDpackage structure 100 also has a good thermal conductivity that helpsthe heat of the blue LEDs 160 be quickly dissipated.

In this embodiment, as indicated by the arrow in FIG. 2, thetransmitting process of the light beams of the white LED packagestructure 100 is as follows. The blue LEDs 160 having variouswavelengths will emit the blue lights within various wavelengths. Theblue lights emitted from the top surface of the blue LEDs 160 will enterthe phosphor structure 170, and pass through the phosphor structure 170to emit upward. The blue lights emitted from the side surface of theblue LEDs 160 will also enter the phosphor structure 170, and then, bereflected by the inclined sidewalls of the cup-structures to emitupward. When the blue lights pass through the phosphor structure 170,one part of the blue lights will be absorbed and be converted into theyellow lights with various wavelengths by the phosphor powders in thephosphor structure 170. The other part of the blue lights will be mixedwith the yellow light to form the white light. Some light reflected bythe inclined sidewalls will pass through the phosphor structure 170 toemit upward. Some light reflected by the inclined sidewalls willencounter the side surfaces of the flattop pyramid of the phosphorstructure 170, and then, the light will be condensed to the center ofthe white LED package structure 100 to be mixed with each other.Therefore, the white light with the blue lights having variouswavelengths can be produced, and the white light having high colorrendering is also created.

Please refer to FIG. 4. FIG. 4 is a cross-sectional schematic diagramillustrating a white LED package structure having a silicon substrateaccording to another embodiment of the present invention. Forconvenience, like elements will not be detailed redundantly. The whiteLED package structure 200 of this embodiment comprises a siliconsubstrate 210, a reflective layer 220, a transparent insulating layer230, a conductive layer 240, four blue LEDs 250 and a phosphor structure260, wherein the conductive layer 240 is disposed on the transparentinsulating layer 230 and electrically connected to the external circuits(not shown in figure). Each blue LED 250 is respectively disposed on theconductive layer 240 in each cup-structure on the silicon substrate 210by flip chip process.

In summary, the present invention provides the white LED packagestructure having four blue LEDs with various wavelengths that arerespectively disposed in four cup-structures on the silicon substrate.The adjacent cup-structures are disposed in a short distance betweeneach other, and the cup-structures are arranged in a rectangular array.The blue LEDs are sealed on the same silicon substrate by the phosphorstructure. However, the present invention is not limited to only havefour cup-structures, square-shaped cup-structure and three various kindsof wavelength specifications of the blue LEDs. The white LED packagestructure can have a plurality of the cup-structures on the siliconsubstrate. The top view shape of the cup-structure can be any othergeometric shape. The blue LEDs can have a plurality of variouswavelength specifications.

Please refer to FIGS. 5-10. FIGS. 5-10 are schematic diagramsillustrating a method of making a white LED package structure accordingto a preferred embodiment of the present invention. As shown in FIG. 5,first, a silicon substrate 300 is provided, such as a silicon wafer.Next, an etching process is performed to form a plurality ofcup-structures 310 having inclined sidewalls and arranged in arectangular array. The etching process can be a dry etching process suchas a reactive ion etching (RIE) process or Bosch process or a wetetching process utilizing potassium hydroxide (KOH), tetramethylammonium hydroxide (TMAH) or ethylenediamine-pyrocatechol-water (EDP) asan etching solution. The Bosch process, also known as pulsed ortime-multiplexed etching, alternates repeatedly between standardisotropic plasma etch and deposition of a chemically inert passivationlayer to achieve nearly vertical structures.

The required optical effect of the white light package structure 300 canbe achieved by controlling depth, width, shape and inclined angle of thesidewalls of the cup-structure 310 and etc. As shown in FIG. 6, areflective layer 320 is formed on the top surface of the siliconsubstrate 300 having the cup-structures 310 by performing a process ofsputtering, evaporation or chemical deposition. As shown in FIG. 7, atransparent insulating layer 330 is formed on the reflective layer 320by performing a process of sputtering, evaporation or chemicaldeposition. As shown in FIG. 8, then, a plurality of metal bumps 340 areformed on the transparent insulating layer 330 in each cup-structure 310by performing a process of deposition or electroplate combined with thelithographic and etching process or lift off process. At the same time,a plurality of electrodes 350 is formed on the transparent insulatinglayer 330 between the adjacent cup-structures 310. As shown in FIG. 9, aplurality of blue LEDs 360 are respectively bonded on the metal bumps340 in each cup-structure 310 by performing a die attachment using glassfrit. Then, each blue LED 360 is respectively connected electrically tothe electrodes 350 through wires 370 by ultrasonic wire bonding method.Last, as shown in FIG. 10, the phosphor powders corresponding to thewavelengths of the blue LEDs 360 are mixed with each other and are addedto a sealing material. Then, a phosphor structure 380 is formed on thecup-structures 310 by performing a sealing process, wherein the sealingprocess is a molding process or encapsulating process. A white LEDpackage structure is thus completed.

Please refer to FIGS. 11-16. FIGS. 11-16 are schematic diagramsillustrating a method of making a white LED package structure accordingto another preferred embodiment of the present invention. Forconvenience, like process the same as the mentioned above will not bedetailed redundantly. As shown in FIG. 1, first, a silicon substrate 400is provided, such as a silicon wafer, and then, an etching process isperformed to form a plurality of cup-structures 410 having inclinedsidewalls and arranged in a rectangular array. As shown in FIG. 12, areflective layer 420 is formed on the top surface of the siliconsubstrate 400 having the cup-structures 410 by performing a process ofsputtering, evaporation or chemical deposition. As shown in FIG. 13, atransparent insulating layer 430 is formed on the reflective layer 420by performing a process of sputtering, evaporation or chemicaldeposition. As shown in FIG. 14, then, a conductive layer 440 is formedon the transparent insulating layer 430 by performing a process ofdeposition or electroplate combined with the lithographic and etchingprocess or lift off process. As shown in FIG. 15, the blue LEDs 450 arerespectively bonded on the conductive layer 440 in the cup-structures410 by performing a flip chip attachment. Last, as shown in FIG. 16, thephosphor powders corresponding to the wavelengths of the blue LEDs 450are mixed with each other and added to a sealing material, and then, aphosphor structure 380 is formed on the cup-structures 410 by performinga sealing process, completing the white LED package structure.

In summary, the present invention provides a method of making the whiteLED package structure. The present invention utilizes a specific etchingprocess to form the required cup-structures on the silicon substrate.Then, the present invention utilizes a microelectromechanical process ofelectroplate or deposition or the semiconductor process to form somelayers that can provide electrical connection and light reflection. Thepresent invention combines above-mentioned process with an LEDmanufacturing process that includes the die attachment, the wire bondingand the sealing process. The white LED package structure having the blueLED with various wavelengths that are mixed with each other can beperformed so as to have the characteristic of high color rendering andcolorful tone.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

1. A white LED package structure having a silicon substrate comprising:a silicon substrate having a plurality of cup-structures thereon, and adistance between the adjacent cup-structures is substantially less than10 micrometers; a reflective layer covering a top surface of the siliconsubstrate; a transparent insulating layer covering the reflective layer;a plurality of metal bumps respectively disposed on the transparentinsulating layer in each cup-structure; a plurality of electrodesdisposed on the transparent insulating layer between the cup-structures;a plurality of blue LEDs having a plurality of various wavelengths,respectively disposed on each metal bump in each cup-structure, and theblue LEDs electrically connected to the electrodes; and a phosphorstructure covering the cup-structures of the silicon substrate, thephosphor structure comprising a plurality of kinds of phosphor powdersand a sealing material, and each kind of the phosphor powder capable ofconverting blue light within certain wavelength into yellow light. 2.The white LED package structure of claim 1, wherein a top view shape ofeach cup-structure is geometric.
 3. The white LED package structure ofclaim 1, wherein the cup-structures are arranged in a rectangular array.4. The white LED package structure of claim 1, wherein the wavelengthsof the blue LEDs comprises three specifications, 450±5 nm, 460±5 nm and470±5 nm.
 5. The white LED package structure of claim 1, wherein a shapeof the phosphor structure is a flattop pyramid-shaped, a top surface ofthe flattop pyramid is flat, and sidewalls of the flattop pyramid areinclined.
 6. The white LED package structure of claim 1, whereinsidewalls of each cup-structure are inclined.
 7. The white LED packagestructure of claim 1, wherein the reflective layer is a metal or anoptical film.